CompTIA A+ Certification All-in-One Exam Guide

Figure 6-18 Expansion slots connecting to chipset
Figure 6-19 Expansion slots connecting to both CPU and chipset
The chipset provides an extension of the address bus and data bus to the
expansion slots, and thus to any expansion cards in those slots. If you plug a
hard drive controller card into an expansion slot, it functions just as if it were
built into the motherboard, albeit with one big difference: speed. As you’ll
recall from Chapter 3, the system crystal—the clock—pushes the CPU. The
system crystal provides a critical function for the entire PC, acting like a drill
sergeant calling a cadence, setting the pace of activity in the computer. Every
device soldered to the motherboard is designed to run at the speed of the
system crystal. A 200-MHz motherboard, for example, has its chipset chips
all timed by a 200-MHz crystal (see Figure 6-20).
Figure 6-20 The system crystal sets the speed.
Clock crystals aren’t just for CPUs and chipsets. Pretty much every chip in
your computer has a CLK wire and needs to be pushed by a clock chip,